Philadelphia ? Bob Willette clocks 110 miles each week on his road-racing bike, mostly while he commutes the 26-mile round trip to work.

He also whacks tennis balls with his doubles group. And he pushes himself in a regular hoops game, where “something’s always twisted or stubbed. Or bleeding,” he said.

The trim North Coventry, Pa., scientist is 53 years old. As with many baby boomers, his physical regimen comes at a price — upper-back pain, tendinitis and various aches. At least once a year, he said, his body “breaks down,” forcing a doctor visit for a round of anti-inflammatories.

Diagnosis? Boomeritis.

Coined by a local orthopedic surgeon, the informal term describes the swelling number of boomers — the oldest are 63 this year — plagued by twinges and pangs and even serious injuries that have not been seen at these levels before.

This is the generation, 78 million strong, intent on staying forever young. Not everyone does Botox. Many in the over-45 crowd stay fit through rigorous exercise that can wear the kids out even as the costs to those seasoned bodies mount.

Sore shoulders, inflamed tendons, arthritic knees.

“People like myself are trying to hold back the clock,” said Nicholas DiNubile, 57. The Havertown, Pa., orthopedic surgeon is credited with first using boomeritis (now trademarked by him) to describe the growing number of middle-age patients with exercise-related ailments. “Baby boomers are the first generation in droves trying to stay active in an aging frame.”

An adjunct professor of orthopedics at the University of Pennsylvania and avid tennis player who has issues with his own knee, DiNubile co-wrote “FrameWork: Your 7-Step Program for Healthy Muscles, Bones, and Joints” in 2005, which argues that the body’s musculoskeletal frame was designed for only 40 years of pounding activity. Yet over the last century, life expectancy has risen more than 50 percent. The U.S. rate is at a record high of nearly 78 years, according to the Centers for Disease Control and Prevention.

Evolution hasn’t, well, evolved fast enough.

“I believe we’ve outlived our warranty,” said DiNubile, who teaches a course on “Boomeritis — Care of the Mature Athlete.”

Baby boomer boo-boos

Statistics on exercise injuries specifically among boomers are slim. But a look at data on emergency room visits paints a picture of a generation sore and bruised.

The U.S. Consumer Product Safety Commission analyzed for The Philadelphia Inquirer its National Electronic Injury Surveillance System data. It estimated that in 2008, ERs treated 282,476 injuries among baby boomers (those ages 44 to 62) who suffered all sorts of sports- and exercise-related misfortune — a 47 percent increase from a decade earlier.

Among the national cases: A 46-year-old man fell off his bike at an indoor track and fractured a shoulder. A 61-year-old woman suffered multiple sprains from leg lifts. A 55-year-old suffered skull and pelvis fractures after falling from his bicycle while preparing for a 150-mile, round-trip bike ride to raise money for causes related to multiple sclerosis.

Another consumer commission study found that among 45-to-64-year-olds, unintentional overexertion was the second-leading cause of nonfatal injuries treated in ERs in 2007.

“Some of it is inevitable,” said Michael Goodyear, chairman of emergency medicine at Riddle Memorial Hospital in Middletown Township. “As we age, our body gets wear and tear.”

Goodyear said about four or five baby boomers — a mix of weekend warriors and exercise fanatics — show up at the ER every day with pulled muscles, bum knees, sprains, strains or more. He advises that “if in your prom picture you’re wearing ruffles and a big old bow tie and an Afro, then keep in mind that you can’t do the same things as you did at that time.”

That message isn’t well-heeded. Frederick Azar, spokesman for the American Academy of Orthopaedic Surgeons, used to treat mostly people in their teens, 20s and 30s in his practice at the University of Tennessee’s Campbell Clinic. “Now, you’ll see patients in the adolescent ages all the way up to the 70s.” Often he sees “a young person’s injury in an older person’s body.”

Cathe Friedrich, 45, co-owner of Four Seasons Health Club in Glassboro, N.J., and an instructor, had inflamed tissue in a knee from daily hammering in the aerobics studio. DiNubile operated in 2006.

“After 40, the injuries start creeping up faster,” she said.

Overuse is one of the main causes. At the same time, the benefits of exercise come from pushing limits. “It’s a fine line,” Friedrich allowed. “As we get older, that fine line gets finer.”